1. Field of the Invention
The present invention relates to an apparatus for attacking microbes, namely, bacteria, viruses, and fungi. More particularly, the present invention is a sustained release galvanic current bandage or gauze for use as a wound dressing.
2. Description of Related Art
The art of applying a low voltage electric current to control microbes and promote healing action for medical and hygienic purposes has been developing for many years. In particular, it is known that the use of a low voltage electric field applied through a reservoir can be used to deliver drugs or agents in the reservoir systematically or to produce a localized therapeutic effect. Moreover, the application of electricity to the body, with or without drugs or agents, can be used therapeutically. Direct current fields can exert a microbicidal effect, and electric voltage can also, via electrophoresis, induce agents or medications to penetrate tissue more deeply, and can induce the agents to penetrate structures or implants such as biofilms. Further therapeutic effects of electricity include control of pain, edema and acceleration of wound healing. Moreover, the localized effect of drugs and agents can be greater at the delivery site than the effect that is seen with topically or systemically delivered agents alone, due to higher available concentrations at the site, over time.
Silver has been used as a disinfectant for centuries. The use of medicinal silver was diminished by the advent of more versatile and effective antibiotics. The misuse of antibiotics coupled with bacteria's ability to mutate have resulted in resistant organisms and reawakened interest in silver's effective antimicrobial properties. Elemental silver is an effective microbicide in solutions as dilute as one part per 100 million. Silver ions kill micro-organisms by blocking the respiratory system, which is the process of harvesting energy by transferring electrons from an electron donor to an electron receptor.
Although salts of silver will immediately supply the bactericidal qualities of silver to a wound, they also impair wound healing. Ionic silver decreases the inflammatory process in a wound, decreases edema, and increases blood supply to the wound. Silver alone decreases wound surface zinc, which is required for metalloproteinase (MMP) activity modulation. Silver and zinc together also increase wound calcium which increases the wound re-epithelization rate. Matrix MMPs are a group of proteolytic enzymes that are vital in various modeling repairs and the inflammatory processes of wound healing. There are now 20 MMPs identified. MMPs are dependent on intrinsic zinc ions and extrinsic calcium for full activity in modifying the inflammatory response by binding histidine. MMPs are produced by a number of important cells vital to wound repair. For example, neutrophils, macrophages, keratinocytes, and fibroblasts are expressed in physiologic repair, remodeling and epithelial proliferation in wounds.
Low voltage antibacterial devices are able to infuse charged molecules, i.e., iontophoresis, as well as uncharged molecules into the body, i.e., electro-osmosis. For example, U.S. Pat. No. 5,298,017 to Theeuwes et al. (the '017 patent), which is incorporated herein by reference, describes an iontophoretic process by which drugs are delivered transdermally or transmucosally under the influence of an electrical potential. Iontophoretic devices use two distinct electrodes, with at least one of the electrodes being applied to the body. These devices typically utilize a conventional electric power source, such as a battery, to develop the electric current. In some cases, the power source is located separately from the device and in some cases the power source is integrated into the device. These devices also rely solely on the creation of a discrete ion pathway incorporating the body or tissue to effect an electromotive force via forms defined by the sequence of a first electrode, tissue and a second electrode.
There are devices described in the prior art that rely on the electric field generated by the device itself. The power source generally provides no therapeutic value itself other than to provide the electric current necessary to drive the iontophoretic or electro-osmotic device to deliver an agent that is different from the electrode metals. Further, if the power supply should fail for any reason, the device is typically rendered useless. Also, where the power source is located away from the device, limitations are imposed on patient mobility. Still further, even when the prior art integrates the conventional power source into the device, there are limitations. In particular, the prior art makes it clear that the conventional power source must be protected from short circuiting itself. Consequently, great lengths have been taken to insure that the two electrodes are insulated in order to limit the possibility of a short circuit. Further limitations of these devices include high cost due to wires, electrical insulation, battery failure, problems with user compliance, maintenance, and damage.
In spite of the fact that the use of external power sources is prevalent in the art of iontophoresis and electro-osmosis, it is known to rely exclusively on the electric potential generated by the galvanic couple between dissimilar materials, e.g., a zinc electrode and a silver/silver chloride counter electrode, to deliver a drug. For example, the embodiment of the device illustrated in FIG. 2 of the '017 patent does not use an external power source. While the primary purpose of such devices is to deliver a drug present in a drug reservoir, as a consequence of the galvanic couple, ions of the materials used for the anode and/or cathode are delivered into the body. Unfortunately, because the anode and cathodes of such prior art devices are typically made from materials having a relatively low total surface area, the rate of metallic ion transfer from the metallic electrodes is typically lower than desired for satisfactory therapeutic effects.
As described in U.S. Pat. No. 5,814,094 to Becker et al. (the '094 patent), iontophoretic devices that provide silver ions for wound healing are known. Use of silver-coated nylon as the anode for the iontophoretic device of the device of the '094 patent provides a relatively high total surface area material as the source of silver ions. However, the device of the '094 patent features the use of an external power source connected to the silver-coated nylon anode to generate the electrical potential that drives the silver ions into the body, and so suffers from the limitations of other iontophoretic devices described above.
U.S. Pat. No. 6,522,918 to Crisp et al. (the '918 patent), which is incorporated herein by reference, describes electrolytic devices for use in treating tissue through the use of a silver-bearing material and a metal other than silver with no external voltage source necessary. However, one of the disadvantages of the devices of the '918 patent is that the devices are limited in usefulness due to their inherent short-lived duration of action.
Therefore, a need exists for a wound dressing bandage or gauze that provides a galvanic current for extended periods of time before having to change the bandage or gauze.